Japanese Patent Publication No. 08-103434 (Patent No. 3359756) (referred to as Patent Document 1) discloses a technique in which amounts of change of oxy-hemoglobin densities and amounts of change of deoxy-hemoglobin densities in blood in a plurality of measuring regions of a human brain cortex of a subject are measured, results of the measurement are displayed on a display device, thereby obtaining biological information.
Japanese Patent Publication No. 09-19408 (referred to as Patent Document 2) discloses a technique in which oxy-hemoglobin densities in blood in a plurality of measurement regions of a human brain cortex of a subject are measured, auto-correlation and cross-correlation functions of time-variable changes in relative change amounts of the densities are computed, and a topography image is prepared from the correlation functions at individual measurement points. When the technique disclosed in this publication is used, a local biological function may be measured from the topography image.
In a technique disclosed in Japanese Patent Publication No. 09-149894 (Patent No. 3543453) (referred to as Patent Document 3), and deoxy-hemoglobin densities in blood in a plurality of measurement regions of a subject are measured, thereby obtaining measurement signals. Then, in this technique, a feature parameter is computed from each measurement signal. By determining whether a standard deviation of the feature parameter and an average value of the feature parameter belong to a distribution (a measurement region) of a standard deviation of predetermined reference data and an average value of the predetermined reference data, a brain function activity is measured. This publication shows that a neural network is employed as a method of the determination.
Japanese Patent Publication No. 11-311599 (referred to as Patent Document 4) discloses a specific optical measurement technique that may be employed when auto-correlation and cross-correlation functions of time-variable changes in relative change amounts of oxy-hemoglobin densities in blood in a plurality of measurement regions of a human brain cortex of a subject are computed, and a topography image is prepared from the correlation functions at individual measurement points, as in Patent Document 2.
Japanese Patent Publication No. 2000-237194 (referred to as Patent Document 5) discloses a specific technique related to the techniques disclosed in Patent Documents 2 and 4, which is employed when a result of measurement is displayed on a display device.
Further, WIPO International Publication No. WO2002-32317 (Patent Document 6) discloses a technique in which a time-variable change amount of a hemoglobin density is displayed on display means in the form of a graph associated with a positional relationship between optical irradiation means and optical detection means.
Japanese Patent Publication No. 2003-365445 (referred to as Patent Document 7) discloses a technique in which a ratio of a deoxy-hemoglobin density to an oxy-hemoglobin density is measured, and whether a mammal is stressed or relaxed is determined from a result of the measurement.
Japanese Patent Publication No. 2004-229948 (referred to as Patent Document 8) discloses a technique in which, by analyzing a change rate of a hemoglobin density, information on a degree of density of a subject is obtained, thereby determining a condition at a time of learning.
Japanese Patent Publication No. 2004-184402 (referred to as Patent Document 9) describes an appropriate relationship among a measurement period of a hemoglobin density, a task supplied to a subject, and a rest supplied to the subject.
Japanese Patent Publication No. 2004-170958 (referred to as Patent Document 10) proposes a technique in which at least a deoxy-hemoglobin amount in blood in a measurement region of a subject is measured in time series, and a learning level of work by the subject is determined from time-variable change data of the deoxy-hemoglobin amount.
Japanese Patent Publication No. 2004-194924 (referred to as Patent Document 11) discloses a technique of quantitatively measuring a brain function including emotion using an electroencephalogram.
Two documents propose a technique in which using near-infrared spectroscopy, a change in a brain blood flow caused by brain activity is observed, and a brain active region and a temporal variation of the brain activity are thereby measured. [Nonpatent Document 1: Mamoru Tamura, “Brain Function Measurement Using Near-infrared Light”, Journal of the Society of Instrument and Control Engineers, Vol. 42, No. 5, pp. 396-401, (2003.5) and Nonpatent Document 2: Hideaki Koizumi, Atsushi Maki, Takeshi Yamamoto, Hideo Kawaguchi, Fumio Kawaguchi, Noriyoshi Ichikawa, “Brain Function Measurement Using Optical Topography”, Journal of the Society of Instrument and Control Engineers, Vol. 42, No. 5, pp. 402-407, (2003.5)].    Patent Document 1: Japanese Patent Publication No. 08-103434    Patent Document 2: Japanese Patent Publication No. 09-19408    Patent Document 3: Japanese Patent Publication No. 09-149894    Patent Document 4: Japanese Patent Publication No. 11-311599    Patent Document 5: Japanese Patent Publication No. 2000-237194    Patent Document 6: WIPO International Publication WO2002-32317    Patent Document 7: Japanese Patent Publication No. 2003-365445    Patent Document 8: Japanese Patent Publication No. 2004-229948    Patent Document 9: Japanese Patent Publication No. 2004-184402    Patent Document 10: Japanese Patent Publication No. 2004-170958    Patent Document 11: Japanese Patent Publication No. 2004-194924    Nonpatent Document 1: Mamoru Tamura, “Brain Function Measurement Using Near-infrared Light”, Journal of the Society of Instrument and Control Engineers, Vol. 42, No. 5, pp. 396-401, (2003.5)    Nonpatent Document 2: Hideaki Koizumi, Atsushi Maki, Takeshi Yamamoto, Hideo Kawaguchi, Fumio Kawaguchi, Noriyoshi Ichikawa, “Brain Function Measurement Using Optical Topography”, Journal of the Society of Instrument and Control Engineers, Vol. 42, No. 5, pp. 402-407, (2003.5)